A cyclic heptadecapeptide which induces melanosome aggregation within fish melanophores was isolated from salmon pituitary glands, see Kawauchi, H. et al., Nature, 305, 321-323 (1983), and it was named melanin concentrating hormone (MCH). Fish MCH has been reported to have the opposite effect, i.e., causing dispersal of melanosomes, in amphibians, Wilkes, B. C. et al., B.B.R.C., 112, 613-619 (1984). MCH is believed to be synthesized in the neurons of the hypothalamus and translocated into the neurohypophysial tissues. MCH immunoactivity has been reported in hypothalamic extracts of the rat: Baker et al., Gen. Comp. Endocrinol., 50, 423-431 (1983) and Naito, N. et al., Cell Tissue Res., 253, 291-295 (1988). Very crude extracts of an MCH-like substance from the rat hypothalamus showed a generally parallel response to fish MCH in a radioimmunoassay (RIA) using an antiserum directed against salmon MCH, even though the material appeared to have distinct chromatographic properties and showed multiple immunoreactive peaks, not all of which showed bioactivity, Zamir, N. et al., P.N.A.S. USA, 83, 1428-1531 (1986); Sekiya, K. et al., Neuroscience, 25, 925-930 (1988); Naito, N. et al., (1988) supra.
Despite all of this work over a period of several years, the mammalian hormone remains unisolated and uncharacterized, and as a result, true testing of the biological activity of mammalian MCH has not heretofore been possible. As a result, great efforts were made to isolate, purify and then characterize and test mammalian MCH.